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Co-authored-by: Ralf Jung <post@ralfj.de>
This commit is contained in:
Camille Gillot 2023-10-27 20:51:25 +02:00 committed by GitHub
parent 856161886a
commit 24be43356e
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2 changed files with 12 additions and 6 deletions
compiler
rustc_middle/src/mir
consts.rs
rustc_mir_transform/src
gvn.rs

11
compiler/rustc_middle/src/mir/consts.rs

@ -174,10 +174,13 @@ impl<'tcx> ConstValue<'tcx> {
}
/// Check if a constant may contain provenance information. This is used by MIR opts.
/// Can return `true` even if there is no provenance.
pub fn may_have_provenance(&self, tcx: TyCtxt<'tcx>, size: Size) -> bool {
match *self {
ConstValue::ZeroSized | ConstValue::Scalar(Scalar::Int(_)) => return false,
ConstValue::Scalar(Scalar::Ptr(..)) => return true,
// It's hard to find out the part of the allocation we point to;
// just conservatively check everything.
ConstValue::Slice { data, meta: _ } => !data.inner().provenance().ptrs().is_empty(),
ConstValue::Indirect { alloc_id, offset } => !tcx
.global_alloc(alloc_id)
@ -504,10 +507,10 @@ impl<'tcx> Const<'tcx> {
/// Return true if any evaluation of this constant always returns the same value,
/// taking into account even pointer identity tests.
pub fn is_deterministic(&self) -> bool {
// Some constants may contain pointers. We need to preserve the provenance of these
// pointers, but not all constants guarantee this:
// - valtrees purposefully do not;
// - ConstValue::Slice does not either.
// Some constants may generate fresh allocations for pointers they contain,
// so using the same constant twice can yield two different results:
// - valtrees purposefully generate new allocations
// - ConstValue::Slice also generate new allocations
match self {
Const::Ty(c) => match c.kind() {
ty::ConstKind::Param(..) => true,

7
compiler/rustc_mir_transform/src/gvn.rs

@ -917,6 +917,7 @@ fn op_to_prop_const<'tcx>(
// Do not try interning a value that contains provenance.
// Due to https://github.com/rust-lang/rust/issues/79738, doing so could lead to bugs.
// FIXME: remove this hack once that issue is fixed.
let alloc_ref = ecx.get_ptr_alloc(mplace.ptr(), size).ok()??;
if alloc_ref.has_provenance() {
return None;
@ -928,6 +929,8 @@ fn op_to_prop_const<'tcx>(
if matches!(ecx.tcx.global_alloc(alloc_id), GlobalAlloc::Memory(_)) {
// `alloc_id` may point to a static. Codegen will choke on an `Indirect` with anything
// by `GlobalAlloc::Memory`, so do fall through to copying if needed.
// FIXME: find a way to treat this more uniformly
// (probably by fixing codegen)
return Some(ConstValue::Indirect { alloc_id, offset });
}
}
@ -939,7 +942,7 @@ fn op_to_prop_const<'tcx>(
// Check that we do not leak a pointer.
// Those pointers may lose part of their identity in codegen.
// See https://github.com/rust-lang/rust/issues/79738.
// FIXME: remove this hack once https://github.com/rust-lang/rust/issues/79738 is fixed.
if ecx.tcx.global_alloc(alloc_id).unwrap_memory().inner().provenance().ptrs().is_empty() {
return Some(value);
}
@ -969,7 +972,7 @@ impl<'tcx> VnState<'_, 'tcx> {
// Check that we do not leak a pointer.
// Those pointers may lose part of their identity in codegen.
// See https://github.com/rust-lang/rust/issues/79738.
// FIXME: remove this hack once https://github.com/rust-lang/rust/issues/79738 is fixed.
assert!(!value.may_have_provenance(self.tcx, op.layout.size));
let const_ = Const::Val(value, op.layout.ty);